During the Polish Antarctic Geodynamic Expeditions, 1979-91, a wide
geophysical and geological programme was performed in the transition
zone between the Drake and South Shetland microplates and the Antarctic
Plate, in West Antarctica. In the Bransfield Strait area, and along
passive continental margin of the Antarctic Peninsula, 20 deep seismic
sounding profiles were made. The interpretation yielded two -
dimensional models of the crust and lithosphere down to 80 km depth. In
the coastal area between the Palmer Archipelago and the Adelaide Island,
the Earth's crust has a typical continental structure. Its thickness
varies from 36 to 42 km in the coastal area, decreasing to about 25-28
km toward Pacific Ocean. In the surrounding of Bransfield Strait, the
Moho boundary depth ranges from 10 km beneath the South Shetland Trench
to 40 km beneath Antarctic Peninsula. The crustal structure beneath the
Bransfield Strait trough is highly anomalous. Presence of a
high-velocity body, with longitudinal seismic wave velocities Vp > 7,0
km/s, was detected there in the 6-32 km depth range. This inhomogeneity
was interpreted as an intrusion, coinciding with the Deception-Bridgeman
volcanic line. In the transition zone from the Drake Passage to the
South Shetland Islands, a seismic boundary in the lower lithosphere
occurs at a depth ranging from 35 to 80 km. The dip of both the Moho and
this boundary is approximately 25° towards the southeast, indicating the
direction of subduction of the Drake Plate lithosphere under the
Antarctic Plate. Basing on the results of four Polish Geodynamic
Expeditions, the map of crustal thickness in West Antarctica is
presented.